Exporting to Unity - How do you get a single FBX to support multiple materials?
Each material you assign in Blender, will be a material in Unity.

It looks you already have that, if Unity has generated all those material slots. You will just need to re-assign the colour in Unity, or attach the texture you've used if I read your question correctly.



Each face has a different material on it, 3 materials in Blender, Unity will read that and create three materials for those faces.